1. Field of the Invention
The present invention relates to an internal focus lens that suitable for photographic cameras, video cameras, etc. and has an anti-vibration function.
2. Description of the Related Art
A large number of internal focus lenses that can be used in photographic cameras and video cameras and that have an anti-vibration function of correcting image blur consequent to vibrations, such as hand-shake, have been proposed (see, for example, Japanese Patent Nos. 3541283 and 4272725).
The internal focus lens recited in Japanese Patent No. 3541283 includes sequentially from an object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power, where the second lens group is moved to perform focusing and the third lens group is moved orthogonally with respect to the optical axis to correct image blur.
The internal focus lens recited in Japanese Patent No. 4272725 includes sequentially from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power, where the second lens group is moved to perform focusing and a portion of the lenses included in the third lens group are moved orthogonally with respect to the optical axis to correct image blur.
In optical systems having the conventional anti-vibration function, the lens group (anti-vibration group) responsible for image blur correction is often configured by multiple lenses. In both of the internal focus lenses disclosed in Japanese Patent Nos. 3541283 and 4272725, the anti-vibration group is configured by multiple lenses and thus, is heavy. Consequently, since the actuator also has to be larger in order to drive the anti-vibration group, the size of the lens barrel supporting the lens also unavoidably becomes larger. Further, since image blur correction coefficients in either optical system are small, the anti-vibration group has to be moved over a longer distance to correct image blur and therefore, with respect to a dimension along the diameter of the optical system, a large space is required, arising in a problem that the size of the lens barrel supporting the optical system increases.